Skip to main content
Tool Factory

Numbers, Units & Calculators

Byte Addition Calculator

Add a repeating key to bytes from text, wrapping each sum modulo 256. Review decimal byte values.

Tool workspace

Your input stays in this browser.

Add the required input to continue.

Needs input

You can run the tool again after any change.

Enter literal text. Characters through U+00FF use one byte each. Any other character makes the whole input use UTF-8.

Options

Your result appears here

Add a repeating key to bytes from text, wrapping each sum modulo 256. Review decimal byte values.

This tool runs open-source code from CyberChef by GCHQ (Apache License 2.0). See open-source credits.

Byte Addition Calculator adds each key byte to the corresponding input byte, modulo 256. It converts source text into bytes before the operation. The result lists decimal byte values.

The result lists decimal byte values from 0 through 255. Copy and Save preserve the array representation.

  • Inspect a small byte transformation with a known input and expected result.
  • Compare repeating key bytes with ASCII input bytes.
  • Check a step before adding it to a recipe.

Instructions

  1. Enter literal text in Text input. Start with ABC.
  2. Choose Hex under Key format and enter 01 in Key. The key repeats across the input bytes.
  3. Review the decimal byte array. The example produces [66,67,68]. Copy or save the result.

Example

Input: ABC

Settings: Key format Hex; Key 01

Result: [66,67,68]

The key repeats across the input bytes. Key 0102 gives [66,68,68].

Limits

  • Text input preserves literal characters. For example, 41 means two text bytes, [52,49], rather than hexadecimal byte 0x41.
  • Characters from U+0000 through U+00FF use one byte each. Any other character makes the whole input use UTF-8.
  • For example, é becomes [233], while éĀ becomes [195,169,196,128]. These values describe this tool's input conversion.
  • Key format changes only the key. An empty key acts as byte 0; it leaves addition and subtraction unchanged but clears AND results.
  • Use values from 0 through 255 for Decimal keys.
  • The source field does not parse hexadecimal byte pairs. For binary input, use Hex Decoder before this operation in the recipe workspace.
  • The result is a byte array, not a Unicode code-point list. These byte operations do not provide secure encryption.

Questions

Does Text input read hexadecimal numbers?

No. It reads literal text, including spaces and line breaks. For example, 41 becomes input bytes [52,49], not hexadecimal byte 0x41.

How does the tool convert non-ASCII text into bytes?

Characters from U+0000 through U+00FF use one byte each. Any other character makes the whole input use UTF-8. For example, é becomes [233], while éĀ becomes [195,169,196,128].

Does Key format change the source input?

No. Key format applies only to Key. Choose Hex, Decimal, Binary, Base64, UTF8, or Latin1. The key bytes repeat across the input. Use values from 0 through 255 for Decimal keys.

What happens with an empty key?

An empty key acts as byte 0. Adding or subtracting 0 leaves each input byte unchanged.

How do I use binary data and save the result?

For binary input, use Hex Decoder before this operation in the recipe workspace. The standalone result lists decimal byte values. Copy and Save preserve the array representation; they do not convert it to readable text.